The present invention relates to a method for continuously producing a reinforced hose having a plurality of reinforcement layers without using a core member or a protective cover for a rubber sheath.
An example of such a method for producing high-pressure hoses having braided reinforcement layers without using a core member or a protective cover for a rubber sheath is disclosed in Japanese Patent Application Publication No. 4-3,737. In the disclosed method, a hose formed by an extruder is pulled at a speed higher than the extruding speed of the extruder through a hardening device.
With this method, by the higher pulling speed the hose made of an elastomer is elongated to change braided angles of reinforcement members to angles slightly less than a predetermined angle. By releasing the pulling, forces acting upon the hose the reinforcement members are restored toward their original shapes to obtain the predetermined optimum braided angles.
However, such a prior art method is employed for producing a hose having a single reinforcement layer. Even if the method could be applied to the production of hoses having plural braided reinforcement layers, the joint strength between the plural reinforcement layers of produced hoses is not increased sufficiently. Therefore, it is impossible to improve effectively the pressure-resistance of reinforced hoses produced according to the prior art method.
In greater detail, a hose having plural, for example two reinforcement layers is generally designed to have average braided angles of these reinforcement layers substantially equal to the angle of repose (54.degree.44'). This is to prevent the entire hose from elongating and contracting upon being subjected to inner pressure and to exhibit its pressure-resistance in cooperation with the inner and outer reinforcement layers by permitting the inner reinforcement layer to be expanded and the outer reinforcement layer to be contracted upon being subjected to the inner pressure.
In other words, it is usual to design the hose in a manner that braided angles of inner reinforcement layers are less than the angle of repose and braided angles of outer reinforcement layers are greater than the angle of repose. Therefore, when the hose having inner and outer reinforcement layers is pulled in unvulcanized state by a pulling speed so that the average braided angles are about 53.degree. according to the prior art, the inner reinforcement layer inherently having the smaller braided angles and the outer reinforcement layer inherently having the larger braided angles are simultaneously pulled so that the contraction in diameter of the inner reinforcement layer becomes larger than that of the outer reinforcement layer. As a result, the clearance between the inner and outer reinforcement layers becomes larger than its initial value. In the prior art method performing the vulcanization of unvulcanized rubber during pulling the hose with such a pulling speed, it is, therefore, impossible to join the inner and outer reinforcement layers with a sufficient joining force.